Spark plug



UnitedStates Patent O "me PLUG A, l l l v --wufreda `Byannsky,.irum.arr-1mi, and mma tondeuse,

Flint, Mich., hassignors to General tMotors Gor-poration, vDetroit, .=Mich., a .corporation ...of .Delaware Application January 1951954*Sei'lailflor34042878 zvcnims. toners-.144),

'Ihis inventionnrlates to spaikplugs, and `more particularly, to -spark plug'sbt the-type'f'having a metal shielded insulator and used,primarilyz-infaircraftaengines.

:Such aircraft. spark ,plugs .have ansinsula'tor with? ani upper portionwhich is tubular in 'shape forivthereception 'cof anignitioncable. This, tubular insulator portion :is .fprotectedfby ametal shielding barrelfthealower end 'ofi-which is `-secured-to the spark plug shell. .'.eIt hasiheretofo're been the practice to Ysecure the sshieldi'llg barrel 5to-the spark plug shell .by .brazingor .soldering this being the sole means for holldingMth'etWo parts together. There have been iinstancesofrsuch:azijointfailing duirrgfop'eration of the spark plug due to the shock, vibration and high temperatures encountered, thus resulting in the barrel coming loose from the spark plug shell. Such failures are particularly troublesome because they often occur while the aircraft is in flight and thus present a tremendous safety hazard. Not only is one cylinder of the aircraft engine thereby made inoperative, but also, because of the loose parts which result, serious damage may be caused to other parts of the engine.

It is an object of the present invention to provide an aircraft spark plug which is more durable and more reliable than those heretofore used.

Morespeciiically, it is an object of the present invention to provide a shielded aircraft spark plug with improved means for securing the insulator shielding barrel to the spark plug shell and to provide an improved method for making same.

These objects are carried out in accordance with the invention by the provision of a mechanical lock inaddition to the braze, between the shielding barrel and the spark plug shell. In the preferred embodiment this rnechanical lock is accomplished by a cooperating ange and shoulder arrangement between the joined parts.

Other objects and advantages of the invention will appear more clearly from the following detailed description and from the drawing which shows a cross sectional view of the preferred embodiment.

Referring now to the drawing, there is'shown an aircraft spark plug comprising an elongated insulator member 2 carrying a center electrode assembly 4 in the center bore thereof, a generally tubular metal shell 6 carrying ground electrode 8, and metal vshielding barrel 10 which concentrically surrounds the upper end of the insulator and which is secured to the shell 6 in accordance with the present invention.

The insulator member is provided with a lower shoulder 12 and also with an upper shoulder 14 of slightly larger diameter. The upper end 16 of the insulator is tubularly shaped for the reception of an insulated ignition cable (not shown) having an electrical connector at its lower end to establish electrical contact with the spark plug central electrode assembly.

The central electrode assembly includes metal contact plug 18, resistor element 20, conductive glass seal 22 and ring tip 24 having an upper portion embedded Vin the glass seal 22 and a lower portion extending below1 2,874,323 patented ret. '17,1959

` lthe insulator. The upper portion Y31 vofgthe -shell '-is.of

increased diameter to accommodate vthe insulatorish'oul- 'der 14. f

'The lower end iof Athe shielding barrel 10 is ofsmaller diameter than vthe upper vend of shell .6 'andlis'positioned concentrically therewithin, the tapered lower edge32 of 4theibarrel Acooperatingwithshoulder 14 to maintainithe 'insulator securely andjproperly `positioned within `the fsh'ell. lMetalgaskets 34 and 36 assureafgoodsealrand 'a' rm'seating'ofthe-insulator. y y

vTry-accordance with the'inventiom'the top edgeof'thje shell is turned or bent inwardly "so las to" formfan annular ange 38 vwhich is pressed over and engages an V`externalfannular -shoulderd formed in the shielding barrel. `The Ytop edge of the shell `whichforms an'ge-SS is .preferably fof Y'slightly reduced thickness,'in comparison with the rest of the shell, in order to facilitatefthe turning orbending operation. v`In thezembodimentfshown, Athe 'shoulder 40 4is provided byforming-'anannularlgroove "41.on`the barrel It). This-"cooperatingflange and-shoulder arrangement forms a mechanical lock which assures against loosening of the parts. Additionally, the shield 10 is brazed to the shell as shown at 42. It is preferable to form the insulator 2 with a slightly reduced diameter adjacent the brazing zone, as shown at 46, in order to prevent insulator breakage due to heat shock during the brazing operation.

In manufacturing the spark plug, the insulator 2, with center electrode assembly 4 already secured within the centerbore, is rst positioned in shell 6. A ring of silver solder or other suitable brazing material is Placed in groove 44 which is formed in the lower end of the barrel 10. Then the barrel is seated concentrically within the shell and heat is applied in the vicinity of the ring of brazing material. Capillary action causes the fused brazing material to run out of the groove 44 and between the shell and barrel to form the joint as shown at 42. It is preferable to coat the surfaces on the barrel and shell to be brazed with a suitable linx in order to assist the spreading of the brazing material between the parts.

After the brazing operation is completed, the upper edge of the shell is turned inwardly and over the shoulder 40 to form flange 38. With the parts thus secured, a high amperage current is passed through the shell'to heat and thereby soften the thin section 48 and pressure is simultaneously applied to the ends of the shell. This latter operation collapses thin section 4S thereby wedging insulator shoulders 12 and 14 between the lower edge 32 of the barrel and ridge 36 respectively to tightly secure the insulator within the shell.

It will be obvious that if the distance between insulator shoulders 12 and 14 is too great, or too small, the flange 38 will not properly engage the shoulder 40. Thus where there is to be high production of the spark plug of this invention, itis important that the insulator members used be of relatively uniform size. lf the insulator lengths` vary considerably it may be necessary to machine to proper size the top edge of each spark plug shell just prior to turning it inwardly to form the flange 38.

Aircraft spark plugs made in accordance with the present invention are more durable and more reliable than those heretofore used. The mechanical interlock provided between the shielding barrel andthe shell by means of the ange and shoulder structure assures against loosenlng of the parts even under the most adverse operat ing conditions wherein high temperatures, vibration and mechanical shock are encountered.

It is to be understood that, although the invention has been described with specific reference to a particular embodiment thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as delned by the appended claims.

What is claimed is: t Y Y 1. A spark plug comprising a tubular metal shell carrying a ground electrode at the lower end thereof, said shell having a lower portion of smaller diameter than the top portion thereof and being provided with an internal annular ridge, a metal barrel having a lower portion positioned concentrically within the top portion of said shell and brazed thereto, the upper end of said shell having an annular ange turned inwardly and over a shoulder formed on said barrel to lock said shell and said lbarrel together, an elongated insulator within said shell having a tubular shaped upper portion positioned concentrically within said barrel, said insulator having a lower'shoulder engaging said ridge and an upper shoulder positioned in the top portion of said shell and engaging the lower end of said barrel, and a center electrode extending from the lower end of said insulator in spaced relation to said ground electrode to form a spark gap therewlth.

2. A spark plug comprising a tubular metal shell carrying a ground electrode at the lower end thereof, said shell having a lower portion of smaller diameter than the top portion thereof and `being provided with an internal annular ridge, a metal barrel having a lower portion positioned concentrically within the top portion of said shell and brazed thereto, the upper end of said shell having an annular flange turned inwardly and over a shoulder formed on said barrel locking said shell and said barrel together, an elongated insulator within said shell having a tubular shaped upper portion positioned concentrically within-said barrel, said insulator having a lower shoulder engaging .said ridge, an upper shoulder positioned in the vtop portion of said shell and engaging the lower end of said barrel and a portion of reduced diameter adjacent the lower portion of said barrel providing an annular space between said insulator and said barrel, and a center electrode extending from the lower end of said insulator in spaced relation to said ground electrode to form a spark gap therewith.

References Cited in the le of this patent UNITED STATES PATENTS 1,307,910 Ledanois June 24, 1919 2,198,892 Twining Apr. 30, 1940 2,170,765 Nowosielski Jan. 20, 1942 2,379,635 Hastings July 3, 1945 2,416,643 Pinehart Feb. 25, 1947 2,445,777 Hahn July 27, 1948 2,453,048 Tognola Nov. 2, 1948 FOREIGN PATENTS 549,732 Great Britain Dec. 4, 1942 

